The invention relates generally to ultrasonic sandwich transducers of the type producing an astigmatic sonic lobe. Such transducers have at least one small rectangular piezoceramic plate, covered on both sides with one layer of material, whereby the longitudinal side of the ultrasonic sandwich transducer serves as a sound transmission surface and the ultrasonic sandwich transducer is operated on the fourth planar vibrational mode of the small piezoceramic plate. More particularly, the invention relates to such a transducer having improved operating characteristics.
This general type of ultrasonic sandwich transducer is used in wide-angle proximity sensors. The operation of the small piezoceramic plates on the fourth planar vibrational mode enables such structure to achieve a high degree of efficiency for acoustic emission and reception. However, this mode has the disadvantage of generating out of phase vibrations at the longitudinal ends of the sound transmission surface. As a result, strong secondary lobes are generated in addition to the desired narrow sonic lobe in the plane parallel to the orientation of the small piezoceramic plates. This can lead to spurious signals due to interference reflectors lying outside of the principal detecting range.
This invention is directed to the problem of creating an ultrasonic sandwich transducer for wide-angle proximity sensors which is suitable for industrial application, and in which the problems caused by the generation of undesired secondary lobes is reduced.